https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103615
Bug ID: 103615
Summary: [8/9 Regression] wrong code with "-O3" or "-O1
-ftree-vectorize" on x86_64-pc-linux-gnu
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: siarhei.siamashka at gmail dot com
Target Milestone: ---
A reduced testcase from https://codeforces.com/blog/entry/97433
$ cat test.c
int z = 5;
int a[6] = {0, 0, 0, 0, 0, 1};
int main() {
for (int x = 5; x; x--)
for (int y = z; y >= x; y--)
a[y - x] += a[y];
if (a[0] != 7)
__builtin_abort ();
return 0;
}
$ gcc-7.3.0 -O3 test.c && ./a.out
$ gcc-8.3.0 -O3 test.c && ./a.out
Aborted
$ gcc-9.3.0 -O3 test.c && ./a.out
Aborted
$ gcc-9.4.1 -O3 test.c && ./a.out
Aborted
$ gcc-10.3.0 -O3 test.c && ./a.out
Only GCC versions 8.x and 9.x are affected and the bug is triggered by "-O3" or
"-O1 -ftree-vectorize" optimization option.
